The present invention relates to a method for mounting bumped electronic components to a board or substrate.
As a means for mounting electronic parts onto electrodes of a circuit pattern on a board, there has been known a method which forms solder portions, such as solder bumps and solder precoats, on electronic components to be mounted or on electrodes of the board beforehand and joins the electronic components to the electrodes of the board by means of the solder portions. The soldering process involves applying a flux to the solder portions or the electrodes of the board, mounting the electronic components onto the electrodes, and heating and melting the solder to join the solder portions and the electrodes together. After the solder joints have been formed, the assembly is subjected to cleaning to remove flux residues to enhance the reliability after the mounting, followed by filling an underfill resin into gaps between the bumped electronic parts and the board to reinforce the joints. The underfill resin is then hardened by heat treatment, thus completing the mounting process.
The bumped electronic parts mounting process described above, however, poses the following problems as the electronic parts are miniaturized. First, because the use of such solvents as fluorocarbon, which have been in wide use, for cleaning is restricted by law, the cleaning process after soldering has become complicated and risen in cost, which, combined with on-going reductions in the size of electronic components, has contributed to making the cleaning process technically difficult. As to the underfill resin, miniaturization of electronic components reduces the gaps between the electronic components and the board and therefore makes the filling of resin after the mounting of electronic components difficult, resulting in unstable quality of the assembly. In addition to this quality problem, the above conventional mounting method has another problem that it requires two heating processes for the mounting of each component, one for soldering and one for hardening the resin, thus complicating the process.